No point in staying in a relationship you're not interested in being in.

You don't love this girl, you pity her. Thats unfair to both of you, and caring about her means wanting what's best for her.

How would you feel if someone stayed with you out of pity? I'd feel like dirt, that's for sure.

Just because you went all cray-cray after your last break-up, doen't mean she will. Who knows, she may even handle it with grace and finesse.

Please do the decent thing and allow her to find someone who loves her, because you both deserve much better than the BS you're settling for.